Add Host header in http request

http://cbugg.hq.couchbase.com/bug/bug-555 points out that Host
is a required field in HTTP 1.1

Change-Id: I8576796ace691439aac512985fc0d038a20baef7
Reviewed-on: http://review.couchbase.org/25822
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>